Abstract
In this paper, we discuss the development of a beat-to-beat model of the cardiovascular system that qualitatively simulates the characteristic patterns of cardiovascular variability in response to mental task stress. First, we improved Deboer's model by: (1) representing delay function related to the baroreflex as a function of time, (2) setting sympathetic nervous activity and parasympathetic nervous activity as dynamic variables, (3) adding a term describing sympathetic influence and afterload effect on stroke volume, and (4) representing the total effect of the autonomic nervous system on the heart rate by the product of sympathetic influence factor and parasympathetic influence factor. Next, we showed that the presented model can qualitatively reproduce characteristic patterns of cardiovascular variability in response to mental arithmetic stress by decreasing the values of parameters related to parasympathetic nervous activity. The characteristic response patterns are: (a) decrease in heart beat interval, (b) increase in systolic blood pressure, (c) increase in diastolic blood pressure, (d) decrease in heart rate variability (HRV), (e) decrease in amplitude of low-frequency (0.04-0.15Hz) band HRV, and (f) increase in mean frequency of low-frequency band HRV. On the contrary, Deboer's model could not reproduce these patterns by changing the values of parameters related to autonomic nervous activity in a valid manner. Finally, we discuss the generation mechanism of the characteristic patterns of cardiovascular variability in response to mental task stress using the presented model.
